They are 45mm gauge holes, but i hear you can dremmel them out nicely to fit more common 52mm gauges. Infact, i think ive heard somewhere that a company is selling pre modified housings to accept 52mm gauges.

If you do the mod, or find the place selling them, let us know. Im thinking of doing the mod aswell. Ive replaced all the bulbs and leds inside the instrument cluster with blue ones, and in the radio and hvac controls to. So im looking for some decent white faced guages that illuminate blue at night. This isnt ricey is it???? lol

This should sort me out untill i replace all my gauges with an LCD panel connected to an interface with the ECM. If i get this working good, i might sell some kits, but thats a few months in the future.

I'm thinking I'll just mount two gauges in those little steel cups Auto Meter sells. Thats a about a 9 on the rice scale though. Auto Meter also makes the "cobalt" series 2 1/16th gauges. They are LED blue, but black face. They are sharp looking, but they'd better be for the price.